This invention relates to a sprocket for a roller chain, particularly for a roller chain used in an implement to cut, dig, or otherwise remove material. In its preferred embodiment, the sprocket drives a trencher roller chain.
Chainsaws, mining machines, trenchers, and the like use a roller chain to cut, dig or remove material. The chain, which typically carries a series of cutting blades or bits, is entrained around at least one drive sprocket and one idler sprocket. The drive sprocket supports one end of the chain and is coupled to a motor or some other power source to drive the chain. An idler sprocket supports the other end of the chain. If the chain is long, additional idler sprockets may optionally be used at various locations between the ends of the chain.
Various trenchers are known which use the sprocket and chain arrangement described above to dig trenches. These trenches are usually between 2 and 6 feet deep and many yards long. A trench is often dug in order to bury cables or a pipeline. The sprocket and chain arrangement described above allows several cutting passes of the blades or bits attached to the chain within a short amount of time and further facilitates the removal of dirt from the trench.
In many cutting or digging applications, the chain and its supporting sprockets are in constant contact with particulate debris. For example, in the case of a trencher, this particulate debris typically comprises dirt, rocks, and/or sand dug up by the trenching operation. In the case of a chainsaw, the particulate debris typically comprises wood chips and/or sawdust generated by the operation of the chainsaw. In any event, regardless of whether the tool comprises a trencher or a chainsaw, the particulate debris described above frequently gets under the chain rollers between the chain rollers and various surfaces of the sprockets. Since much of this particulate debris is abrasive, this can relatively quickly wear down the sprocket and chain, thereby requiring more frequent replacement of these components than is desirable.
In addition, the particulate debris described above can quickly build up in a layer or coating between the chain rollers and the sprocket. This build up has the effect of increasing the pitch diameter of the sprocket, meaning the chain rollers are forced to ride the sprocket on a larger diameter than normal. The increase in pitch diameter requires the chain to stretch or elongate, which also wears the chain out prematurely.
Moreover, if the pitch diameter increases too much, the chain cannot stretch anymore and it binds. When the chain used on a trencher binds, the trencher chain will not run in the forward digging direction. The operator must then run the trencher chain in reverse to clear the particulate debris buildup.
Several proposals have previously addressed the problem of clearing debris from sprocket and chain areas to prevent premature chain wear and binding. One prior art concept addressing the chain binding problem is that of a variable length chain bar. The chain bar is the support structure the chain travels around. The drive and idler sprockets are located at opposite ends of the chain bar to facilitate motion of the chain. In a variable length chain bar, the chain bar is spring loaded in compression along its lengthwise axis.
When dirt or other debris builds up on the sprocket, the pitch diameter increases and the distance the chain must now travel around the chain bar increases. This results in increasing tension in the chain with the chain potentially binding. However, in a variable length chain bar, the increasing tension in the chain causes the chain bar to shorten. The shortening of the chain bar offsets the extra distance caused by the increase in pitch diameter and relieves the increasing tension in the chain.
While a variable length chain bar postpones chain binding, at some point the chain bar cannot shorten further. In this situation, as dirt and debris continue to build up on the sprocket, the fully shortened chain bar now acts as a rigid chain bar. Consequently, after the chain bar reaches its minimum length, the chain will still bind if dirt and debris continue to build up on the sprocket.
other proposals have focused on the sprocket design. U.S. Pat. No. 3,968,995 to Arentzen shows a roller chain sprocket having dirt gashes or reliefs cut on either face of the sprocket adjacent the bottom of the gullet that receives the chain roller. Each dirt gash or relief extends radially inwardly from the gullet towards the center of the sprocket and is inclined outwardly towards an adjacent face of the sprocket. The purpose of such dirt gash or relief is to xe2x80x9cpromote discharge of dirt from between the rollers and sprocket teeth.xe2x80x9d However, the gullet itself is designed so that the chain rollers engage against the bottom diameter surface of the gullet.
While the use of the dirt gashes or reliefs in the Arentzen patent may be helpful in keeping particulate debris from building up between the chain rollers and the sprockets, it is not completely satisfactory. For example, in a trencher, the volume of debris may be so great that there is insufficient space beneath the chain rollers when the rollers are received in the gullets to accommodate this volume. Thus, debris may still build up beneath the chain rollers despite the presence of the dirt gashes or reliefs.
In addition, particulate debris may also build up on the xe2x80x9cflanksxe2x80x9d of a sprocket tooth between the tooth flanks and the front and back sides of the chain rollers. The dirt gashes or reliefs disclosed in Arentzen are not positioned to promote the discharge of this debris. In other words, any debris that becomes trapped between the front and back sides of the chain rollers and the flanks of the sprocket teeth never reach the dirt gashes or reliefs provided on the sprocket in the Arentzen patent.
In addition, standard sprockets used with roller chains typically have a symmetrical tooth form. Some sprockets for roller chains, such as those shown in U.S. Pat. Nos. 5,876,295 and 5,976,045, have asymmetrical tooth profiles. These asymmetrical tooth profiles are thought to reduce noise in certain roller chain applications such as in automotive engine applications. In these applications, a noisy chain drive would be a problem since it might be heard by the driver or passengers of the vehicle.
However, chain noise is not generally a concern for users of cutting or digging tools, like chainsaws or trenchers, due to the noise generated by the blades or bits during the cutting or digging operation. Accordingly, the sprockets used to drive such chains have typically been sprockets with symmetrically shaped teeth.
One aspect of this invention relates to a material removal implement and a sprocket therefor. The implement comprises a roller chain having a plurality of chain rollers. The roller chain carries a plurality of cutter blades or bits that remove material as the roller chain is driven. A drive sprocket and at least one idler sprocket are provided around which the roller chain is entrained. The drive and idler sprockets each have a plurality of radially outwardly extending teeth that engage against the chain rollers of the chain. A drive system is coupled to the drive sprocket for rotating the drive sprocket in a forward direction to thereby drive the roller chain in a forward direction in which the cutter blades or bits remove material. The drive sprocket has asymmetrically shaped teeth with each tooth having a leading flank and a trailing flank taken with respect to the forward direction of rotation of the drive sprocket. The trailing flank has a larger angle with respect to a radial line extending from a center of the drive sprocket through an apex of the trailing flank than the angle formed between the leading flank and a radial line extending from a center of the drive sprocket through an apex of the leading flank.
Another aspect of this invention relates to a material removal implement and a sprocket therefor. The implement comprises a roller chain having a plurality of chain rollers. The roller chain carries a plurality of cutter blades or bits that remove material as the roller chain is driven. A drive sprocket and at least one idler sprocket are provided around which the roller chain is entrained. The drive and idler sprockets each have a plurality of radially outwardly extending teeth that engage against the chain rollers of the chain. A plurality of gullets are formed between adjacent chain rollers of the chain. A drive system is coupled to the drive sprocket for rotating the drive sprocket in a forward direction to thereby drive the roller chain in a forward direction in which the cutter blades or bits remove material. At least the one drive sprocket further comprises a gap between the bottom of the gullet and the chain roller when the chain roller is in fully engaged contact with the gullet. In addition, the drive sprocket further comprises a pair of first cut-aways. One first cut-away is provided on each face of the drive sprocket extending radially inwardly from the gap and laterally outwardly towards the face of the drive sprocket. The two first cut-aways collectively communicate with the gap to guide particulate debris collecting in the gap to either side of the drive sprocket.
Yet another aspect of this invention relates to a material removal implement and a sprocket therefor. The implement comprises a roller chain having a plurality of chain rollers. The roller chain carries a plurality of cutter blades or bits that remove material as the roller chain is driven. A drive sprocket and at least one idler sprocket are provided around which the roller chain is entrained. The drive and idler sprockets each have a plurality of radially outwardly extending teeth that engage against the chain rollers of the chain. A plurality of gullets are formed between adjacent chain rollers of the chain. A drive system is coupled to the drive sprocket for rotating the drive sprocket in a forward direction to thereby drive the roller chain in a forward direction in which the cutter blades or bits remove material. Means are provided on each face of at least the drive sprocket for helping clear particulate debris tending to collect beneath, in front of and in back of each chain roller.